This invention relates to air control valves or throttle bodies for metering air flow to an internal combustion engine and, more particularly, to a valve with a modified base flow curve.
A conventional throttle body may include a bore, a throttle valve, mechanical linkage for actuating the valve, a throttle position sensor and, possibly, and idle air control actuator for accurately controlling air flow during idle operation. In systems having electronic throttle control, the idle air control function may be performed directly by the electronic throttle control, eliminating the idle air control actuator. To obtain the necessary accuracy in positioning and motion of the valve by an electronic throttle actuator, the bore of the throttle body or air control valve may be shaped. For example, spherical shapes may be applied to the bore above and below the valve to provide finer control of air flow in idle and off idle, or low flow, control portions of a range of throttle positions.
For use in automotive and other applications, throttle bodies for engines are commonly made by die casting to the desired bore configuration. Various sizes of throttle bodies may be provided for application to engines having various requirements for maximum air flow. However, for various engine and vehicle applications, different curves of air flow versus throttle position are often desired in throttle bodies of comparable size, that is having the same maximum air flow capacity.
To provide new die casting dies and tooling for each comparable throttle body for which a modified flow curve is desired would require substantial tooling costs that may not be warranted by the volume of production use of the modified bore configuration. Modified throttle bore configurations for varying the base flow curve of air flow versus throttle position for a standard throttle body by simple machining of the die cast bores would therefore be useful in both production and developmental throttle body applications.
The present invention provides a family of throttle bore configurations modified by machining one or more recesses in a low flow portion of a standard throttle bore. The modified bores provide desired modifications of the throttle body flow curve to meet various application requirements for a particular size, or flow capacity, of a throttle body.
In an exemplary embodiment, a base throttle body is provided with a circular throttle valve rotatable in a range between maximum and minimum air flow positions about a valve axis generally perpendicular to the direction of air flow in a throttle bore or intake passage. In a low flow portion of the range, the passage is defined by a wall having generally spherical control surfaces spaced from the valve periphery with gradually increasing clearance on opposite sides of the valve axis as the valve is opened. In a higher flow portion of the range of throttle valve openings, the valve moves beyond the spherical surfaces to an open bore portion allowing higher air flows, up to a maximum flow.
In accordance with the invention, at least one of the spherical control surfaces is modified by machining into the wall, a recess that interrupts part of the spherical surface. The resulting recessed portion extends from adjacent the minimum air flow position of the valve to an intermediate air flow position at a distal edge of the spherical surface. The recessed portion is of any desired shape suitable for machining and is preferably centered on an axis spaced laterally toward the recessed portion from the throttle valve axis. The recess may be cylindrical, having an outer edge aligned with the internal wall of the throttle body, or passage, at a point laterally opposite the axis of the throttle valve. The size and shape of the recess may be varied. For example, conical, rectangular or other shapes of recesses could be used. The angle of the recess in the bore could also be varied as desired. However, the recess must extend from adjacent the closed throttle position of the valve to modify the full extent of the base air flow curve for the throttle body.
These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings.